At the beginning of the rotary dies, the flat die technique was used, as regards height of the die knives, profiles of said knives, etc., and the cylinder of the anvil or counterdie, was also constructed in steel. This theory was correct and work with the first machines in said conditions was tried, though the first difficulties soon appeared: the knives, coincident with the generatrix of the cylinder, required more pressure for cutting than the circular knives and other disadvantages, which forced the designing of a rotary die which, due to its characteristics made it very costly and unfeasible.
The next step in the evolution of said technique during the last years, consisted in developing a counterdie or anvil of soft and elastic material (elastomers) which permitted the knife to penetrate and to have the sufficient consistency to conduct the cutting of the cardboard.
This phase coincides with the commencement of the development in the industry of polymers and the suppliers are few and the quality low. Under said conditions, this form of cutting evolved and extended rapidly. The anvils, first with the steel base and after with aluminium, was coated with the soft material (elastomer). The soft material used, also improved its characteristics in time, and in parallel, the machines were more rapid each time; the greater rhythm of work made it necessary to change the counterdies a greater number of times, and those anvils, with metallic cores, started to result heavy for an operation which became more frequent each time. Also, the requirements demanded that said changes be conducted in shorter periods of time, thus preventing dead, non productive times of the machine. Another great disadvantage was that once the metallic cores were removed from the machine, they were sent to the elastomer manufacturers to be vulcanized. This process was long, expensive and forced a high number of stored stocks to be available, in provision of long delivery times.
Faced with this new situation, a more versatile practical system was developed in the United States, which consisted in the use of bands. These had two advantages (a more rapid assembly and after use, they are disposable), due to which as from then, and after solving the present problems, the started to have a masive use. This good result, was also due to the improvement of the quality of the raw material used, which continued and currently continues to evolve. The described improvements, compensated in excess the only aspect in which said bands lost efficiency as regards the vulcanization; on becoming a lighter piece and with only one thin steel foil as support, which makes it very manageable, after a time of working in the machine, it losses the initial consistency and the clearance it acquires makes it less reliable than the the same vulcanized material on a more consistent core, this effect having repercussions on the quality of the cutting of the cardboard, and in consequence, on the finished product.
As has been indicated, said bands are discarded after use and in their place a new assembly is placed. Then, both for the manufacturer of the product and for the distributor and user, said formula was perfect. The two latter could maintain an adequate and cost acceptable stock at that moment, indifferent to the disadvantages supposed by the shipments and reshipments of cores for its recovery.
Since approximately eight years ago, other manufacturers of polyurethane anvils (elastomers) after acquiring the technology for the handling of polymers, have introduced innovations in said bands, such as the use of the glass fibre base/support and new hook system which facilitates the interchange of the parts.
Another improvement carried out during the last years, is the use of bushes which rotate freely over the anvil carrier axis. An improvement is thus achieved as regards the wear of the bands and an improved finish of the cut box. The bands are assembled on said bushes, in the same manner as when conducted directly on the cylinder, which gives rise to the previously indicated disadvantages.
These changes were very positive and permitted the increase of the cuota in the Market in a rapid and constant manner. Besides the commented modifications of the bands, it also includes the constant changes in the Market: the most suitable distribution systems, requirements for the use as regards reduction of stocks, needs of obtaining boxes cut with a greater degree of quality, tendency on behalf of the client to attain better prices in purchases, producing margins, at the same time turning more frequently to the Service Companies, so that the same solves the global problems and leaving the responsibility of supplies in their hands, among which the bands of the die-carrier anvil bands are to be found.